This list only tracks new bugs introduced in Beta 1.3+! Do not post old bugs in here! Please read through the whole list and see if a bug you've found is already listed.

Known bugs:

1. Zombies Mobs cannot hurt you sometimes (if they are above or below a layer).
2. Wooden slabs or double wooden slabs don't burn
3. Wooden slabs get destroyed faster with pickaxe instead of an axe.
4. Game may crash upon entering the Nether. When you reload you will be at spawn with no items.
6. Worlds may get corrupted during save format conversion. It is unknown if 1.2 mods have anything to do with this.
7. Levers can be placed on the bottom of a block, as long as there is an open space, and a block horizontal to the open space. The lever will act as if placed on the horizontal block, but looks glitched.
8. If someone uses their bed in SMP, other players may get disconnected. (Un-Recognisable Packet ID: 17)
9. F1 in 3rd person mode no longer flips view.
10. When F3 is pressed ingame and you return to menu, it will stay there. You also cannot toggle it in menu like you were able in 1.2_02 etc.
11. Lighting and transparency issues (especially with ice and portals).
12. New slabs won't stack on top of each other like stone slabs do.
13. All slabs have gray particles instead of their material's.
14. A cactus next to a bed cuts the bed in half. This bug has the same behaviour as doors, so it is not considered as a very new bug!
15. Some people are missing sounds completely after the update while their settings are at 100%. (This could have something to do with the "settings don't save" bug, try connecting to any (fake) multiplayer server to save your settings)
16. F3 shows debug code (numbers) on top of animals. (Duh, how did I forget to list this! <_<)
17. If you manage to obtain the top half of a double stone block in your inventory (using inventory hacks), and you mouse over it to get a name, your game crashes.
18. Beds will display the message "You can only sleep at night" if you are too far away from the bed. (At night.) Unconfirmed, some people say you cannot sleep at night at all.
19. Digging a 2x1 hole and placing a bed there causes the bed to glitch ("You cannot sleep here" or "the bed is already occupied" messages)
20. More lighting issues: Place a block above your bed . It will go pitch-black, even if there would be a light-source nearby.

Patched:

1. Crashing issue with singleplayer. Patched in 1.3 (also known unofficially as 1.3_01) and 1.3_01 (also known unofficially as 1.3_02)
2. Item spawning debug code removed. Patched in 1.3
3. Logs will not burn forever. Patched in 1.3
4. Breaking doubleslab result in two slabs instead of the former one slab Patched in 1.3
5. The transitions between deserts and other biomes are normal now. (Instead of the chunks being rotated.) Patched in 1.3
6. Redstone burnout has been fixed. 3 clocks and 1 clocks do not burn out anymore. Patched in 1.3

Suggested bugs:

These bugs are not new or they cannot be considered as bugs.

1. When F3 is on with the graph, open an inventory. The red graph turns gray. Told that this is not a new bug.
2. Light doesn't penetrate stairs anymore. This old bug is still ingame.
3. Doubleslabs don't have names. They've never had. You're not supposed to obtain these anyway.
4. Random cursor error (double-arrow <-> instead of a normal cursor) in menus. Told that this is not a new bug.
5. Large chests may cause crashes when opening them. This is not a new bug! Crashes are most likely caused by use of mods from 1.2 that have not updated.
6. Slimes don't die easily. This bug has existed since earlier versions, and it is not a new bug! Don't suggest me this again, I'm only listing it here to prevent it popping up more.
7. Mobs eat infinite blocks. This has always happened and it's not new.
8. Crouch + Screenshot = crash. This has always happened and it's not new.
9. Cannot use inventory slots. Old bug related to fullsceen.
10. You cannot place torches on halfsteps. Duh, you've never been able to.
11. I'm not sure if it's a bug or not but sometimes mods can spawn in your completely well lit house while sleeping. Monsters can spawn if you go to sleep and there is a way in for the monsters, this is a feature, not a bug.
12. On SMP: Manually open a door, ~clunk~ sound. Use a pressure plate to open the door, ~silence~. Old bug, duh. Been there at least since Beta 1.2.
13. Fences may be invisible, same with stairs. Nothing new here, move on.
14. Slimes spawn on peaceful. Again, always done that. Nothing new. They are not using the monster variable.

1. Zombies Mobs cannot hurt you sometimes (if they are above or below a layer).

16. F3 shows debug code (numbers) on top of animals. (Duh, how did I forget to list this! <_<)

19. Digging a 2x1 hole and placing a bed there causes the bed to glitch ("You cannot sleep here" or "the bed is already occupied" messages)

1 because it makes sense as zombies attack with their arms (which are held up about mid-level), 16 because F3 is the debug toggle, and 19 because there isn't enough room for YOU, even if there is technically enough room for the bed.

3. Wooden slabs get destroyed faster with pickaxe instead of an axe.
13. All slabs have gray particles instead of their material's.

The new slabs are that way because he recycled the code for the stone slabs, and just directed the other textures on top. It was a pretty lazy thing to do, but I can understand why he thought it would be fine.

1 because it makes sense as zombies attack with their arms (which are held up about mid-level), 16 because F3 is the debug toggle, and 19 because there isn't enough room for YOU, even if there is technically enough room for the bed.